During the oxidative coloring of hair, damage to the keratin fibers may occur due to the aggressive agents. In particular, the natural hydrophobicity of the keratin fibers is reduced since the coloring agents must first make the hair penetrable in order to take effect. On the one hand, however, the water-repelling effect is a natural mode of protection for the hair, and on the other hand parameters desired by the consumer, such as shine, suppleness, feel and “fall” of the hair, are closely linked thereto.
In order to overcome the aforementioned disadvantages, so-called pretreatment agents are available on the market, which are said to protect the hair against the aggressive effect. However, said pretreatment agents often weigh down the hair or adversely affect the outcome of the subsequent lightening or coloring of the hair. In particular, the wash fastness of the coloring may be worsened by the pretreatment agent. Also known are numerous aftertreatment agents which attempt to repair the damage to the hair that is caused during the oxidative coloring treatment. However, all of these methods require a multistage application process, specifically the need to apply a further hair treatment agent either before or after the coloring operation. This is often perceived as bothersome by the consumer, since already the oxidative coloring treatment itself, which involves multiple operating steps and a leave-in time of up to 60 minutes, is very time-consuming.
It is therefore desirable to provide an agent and a method for oxidative hair coloring by way of a hair-protecting treatment, which overcomes the aforementioned disadvantages without having a negative effect on the color result of the oxidative coloring treatment. In particular, it is desirable to provide a coloring agent and a method by which the hair is not weighed down and as little damage to the hair as possible occurs. It is also desirable for the hair protection achieved to take as little time as possible and to take place as far as possible together with the coloring step itself.
The use of dicarboxylic acids such as succinic acid in hair care is prior art. These are widely used in shampoos and particularly in conditioners, in order to provide a caring effect. For instance, patent application WO 2005/115314 A1 discloses a method for restructuring keratin fibers, in which the keratin fibers are brought into contact with cystine and with at least one dicarboxylic acid having 2 to 10 carbon atoms, wherein preferred dicarboxylic acids are selected from oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, maleic acid, fumaric acid and sorbic acid, and particular preference is given to succinic acid. Patent application DE 10051774 A1 describes the use of short-chain carboxylic acids having a molecular weight of less than 750 g/mol in cosmetic agents as an active substance for restructuring keratin fibers. Patent application EP 1174112 A discloses hair treatment agents which, besides an organic acid, include as further mandatory constituents an organic solvent, a cationic surfactant and a higher alcohol, and serve for repairing pores in hair.
More recently, agents which are intended to be mixed with coloring compositions for the purpose of protecting fibers and which include dicarboxylic acids have also been offered on the market. With such agents, admittedly no additional hair treatment agent is applied before or after the coloring operation, but the agent must still be mixed with the actual coloring agent prior to application, which likewise means a further operating step and is perceived as bothersome by the consumer.
In view of the above, desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims.